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Capacitive Tape Loop Position Detector

IP.com Disclosure Number: IPCOM000079364D
Original Publication Date: 1973-Jun-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Koski, JA: AUTHOR

Abstract

This tape loop position detector provides a loop position output signal, which is a linear function of loop position. The sensing device is essentially two variable capacitors whose individual capacitances are equal when the loop is at a midposition, with the capacitance of one being a maximum and the other minimum when the loop is at the ends of its position excursions. The total capacity of the sensing device is the sum of the two individual capacitances. This total capacitance is used to control the frequency of oscillation of an oscillator. This oscillator in turn energizes the sensor. A diode demodulator is driven by the resulting current which flows through the two individual capacitors. In this manner, a linear output signal is provided and system's signal gain is independent of sensor gain.

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Capacitive Tape Loop Position Detector

This tape loop position detector provides a loop position output signal, which is a linear function of loop position. The sensing device is essentially two variable capacitors whose individual capacitances are equal when the loop is at a midposition, with the capacitance of one being a maximum and the other minimum when the loop is at the ends of its position excursions. The total capacity of the sensing device is the sum of the two individual capacitances. This total capacitance is used to control the frequency of oscillation of an oscillator. This oscillator in turn energizes the sensor. A diode demodulator is driven by the resulting current which flows through the two individual capacitors. In this manner, a linear output signal is provided and system's signal gain is independent of sensor gain.

Magnetic tape 1 is buffered by vacuum column 2 as it moves between reel 3 and capstan 4. The position of tape loop 5 is sensed by a capacitive sensing device, represented as two variable capacitors C1 and C2. As the loop moves from a midposition, the capacitance values of these two capacitors differentially vary. Nonlinearities in the sensing device, which results from one of the capacitors having a higher maximum capacitance value than the other, is compensated for by automatically shifting the oscillator frequency to a lower frequency.

Oscillator 6 includes sensor capacitors C1 and C2 as its frequency determining element. The fr...